RP-Department of Physics

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Browsing RP-Department of Physics by Subject "Annealing"

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    Impact of Annealing Thin Films In(OH)xSy Growth By Solution Technique
    (Publishing Center Dialog, 2017) Mosiori, Cliff Orori; Magare, Robert; Munji, Mathew
    Indium Hydroxy Sulphide has demonstrated abundance in resources, low prices, nontoxic characteristics, radiation resistance, high temperature resistance, and chemical stability, and therefore it has become an extremely important photoelectric, photovoltaic, and light sensing thin film material. Some treatment on this material include thermal annealing which is a process used for intrinsic stress liberation, structural improving, and surface roughness to control its electro-optical properties. In a qualitative way, annealing modifies surface morphology, intrinsic parameters, and electron mobility with temperature and time. In this work, an explanation on the surface modification of In(OH)xSy thin films when subjected to an annealing process is discussed. Both electrical and optical effects caused by annealing were carried out and characterizations were performed at different annealing temperatures in nitrogen in the temperature range 373–573 K. Using optical measurements data and simulated data, Scout software was employed and the results showed that increasing annealing temperature causes a slight decrease in transmittance with a consequence of modifying the energy band gaps values between 2.79–3.32 eV. It was concluded that annealing influence optical transmittance and resistance of the film make the thin films potential for photovoltaic, and light sensing applications.
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    Influence of surface passivation on optical properties of spray pyrolysis deposited Pd-F:SnO2
    (Science Publishing Group, 2014-09-10) Munji, M. K.; Mwathe, P.M.; Musembi, R. J.; Odari, B.V.; Munguti, Lawrence; Ntilakigwa, Alex Alfred; Nguu, John; Aduda, Bernard; Muthoka, Boniface
    Pd-F:SnO2 thin films have been prepared by spray pyrolysis technique using an alcoholic precursor solution consisting of stannic chloride (SnCl4.5H20), ammonium fluoride (NH4F) and palladium chloride (PdCl2). Optimization on the deposition parameters has been done in order to obtain high quality thin films. The effect of varying the fluorine content on the optical properties of Pd-F:SnO2 thin films were studied. Data for transmittance and reflectance in the wavelength range from 300nm – 2500nm was measured using the solid spec 3700DUV spectrophotometer. The calculated optical band gap of the as prepared thin films has been found to range from 3.8eV to 4.11eV. Fluorine incorporation for Pd-F:SnO2 has been found to have a narrowing effect on the band gap, but at its higher concentration the band gap has been seen to increase. The band gap narrowing is due to the incorporation of F- ions in the crystal lattice therefore giving rise to donor levels in the SnO2 band gap which is an essential characteristic for the gas sensor applications. Both annealing and passivation have been found to have very insignificant change in optical band gap of Pd-F:SnO2
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    Surface passivation effect on CO2 sensitivity of spray pyrolysis deposited Pd-F: SnO2 thin film gas sensor
    (Science Publishing Group, 2014-10-10) Munji, M. K.; Mwathe, P.M.; Musembi, R. J.; Odari, B. V.; Munguti, Lawrence; Ntilakigwa, Alex Alfred; Mwabora, Julius; Njoroge, Walter; Aduda, Bernard; Muthoka, Boniface
    Different thin films samples made of SnO2, F:SnO2, Pd: SnO2 and and co-doped Pd-F: SnO2 were deposited at a substrate temperature of 450oC using optimized doping concentrations of F and Pd, thereafter the samples were annealed and passivated in a tube furnace at 450oC. Optical and electrical methods were used in characterizing the thin film samples: The band gap energy for all samples was extracted from optical data using a proprietary software, Scout™ 98. The calculated band gap energy were found to be 4.1135eV for Pd:SnO2 and 3.8014eV for F:SnO2 being the highest and the lowest calculated band gap energies, respectively. The wide band gap energy has been attributed to the incorporation of Pd ions in crystal lattice of SnO2 thin film for Pd:SnO2 while for F:SnO2 has been due to incorporation of F- ions in the crystal lattice of SnO2 which gives rise to donor levels in the SnO2 band gap. This causes the conduction band to lengthen resulting to a reduction in the band gap energy value. The electrical resistivity was done by measuring the sheet resistance of the SnO2, Pd:SnO2, F:SnO2 and Pd-F:SnO2 thin films. The undoped SnO2 thin film had the highest sheet resistivity of 0.5992 Ωcm while F:SnO2 had the lowest sheet resistivity of 0.0075 Ωcm. The low resistivity of F:SnO2 results from substitution incorporation of F- ions in the crystal lattice of SnO2 thin films, instead of O- ions which lead to an increase in free carrier concentration. The Pd-F:SnO2 gas sensor device was tested for CO2 gas sensing ability using a lab assembled gas sensing unit. The performance of the gas sensor device was observed that: the as prepared device was more sensitive to CO2 gas than those subjected to annealing and passivation. The decrease in the sensitivity of the annealed Pd-F: SnO2 gas sensor is attributed to decrease in grain boundary potential resulting from grain growth. This causes a decrement in adsorption properties of CO- and O- species by the annealed Pd-F: SnO2 thin film. The sensitivity of passivated Pd-F: SnO2 gas sensor was found to be the lowest. The low sensitivity is due to the effects of nitration and decrement in grain boundary potential resulting from grain growth, nevertheless, the sensitivity of the passivated Pd-F: SnO2 thin film wasfound to be within the range for gas sensing applications.